The present invention generally relates to a semiconductor device having a fuse element, and a manufacturing method thereof. More particularly, the present invention relates to a semiconductor device having a fuse element which is formed from a semiconductor layer such as polysilicon, a metal layer such as silicide, or a laminated structure of a semiconductor layer and a metal layer, and a manufacturing method thereof.
Fuse elements have been used in semiconductor devices in order to designate a bit for using a redundant circuit of memory circuitry, to adjust a resistance of analog circuitry, to activate functions of logic circuitry, and the like. By forming a fuse element simultaneously with elements such as a transistor in the same semiconductor device, an electric resistance of the fuse element can be adjusted from the outside after the semiconductor device is manufactured and tested, so that operation of a desired function can be controlled.
A polysilicon fuse element which is electrically blown by laser treatment, an anti-fuse element which is formed between lower and upper electrodes and blown by dielectric breakdown of a thin film insulator, and the like have been used in semiconductor devices. With recent improvement in integration and miniaturization of semiconductor devices, however, such kinds of fuse element are going to be replaced with a fuse element having a polysilicon resistor of an elongated shape. This kind of fuse element is blown by heating the polysilicon resistor to its melting point or higher by Joule heat generated by applying a current to the polysilicon resistor (for example, refer to Japanese Patent Laid-Open Publication No. 2000-40790). Hereinafter, this kind of fuse element is referred to as an electric fuse element in order to distinguish this kind of fuse element from a fuse element which is blown by laser treatment and an anti-fuse element.
In such an electric fuse element, a fuse portion (a portion of a fuse element for isolating circuitry) formed from a polysilicon resistor need not be completely blown. The fuse portion is melted and thinned by heat generated by applying a current, thereby increasing a resistance value.
FIGS. 7A and 7B show a semiconductor device having a conventional electric fuse element. FIG. 7A is a plan view and FIG. 7B is a cross-sectional view taken along line C-C in FIG. 7A. Note that FIG. 7A does not show a first interlayer insulating film 104 and a second interlayer insulating film 108 shown in FIG. 7B. Metal wirings 107a, 107b are shown by dotted line in FIG. 7A.
Referring to the plan view of FIG. 7A, the conventional electric fuse element 103 is formed from a first region 103a, a second region 103b and a third region 103c. The first region 103a serves as a fuse portion. The second region 103b and the third region 103c are provided on both sides of the first region 103a, and each serves as a region where a contact is to be formed (hereinafter, referred to as a contact formation region). The first region 103a of the electric fuse element 103 has a narrower pattern width (a width in the vertical direction of the figure) than that of the second region 103b and the third region 103c. Five contact plugs 106a, 106b are provided in a row in the vertical direction of the figure on the second region 103b and the third region 103c, respectively.
Referring to the cross-sectional view of FIG. 7B, the semiconductor device having the conventional electric fuse element 103 includes a semiconductor substrate 101, an insulating film 102, an electric fuse element 103, a first interlayer insulating film 104, contact holes 105a, 105b, contact plugs 106a, 106b, metal wirings 107a, 107b, and a second interlayer insulating film 108. The insulating film 102 is formed on the semiconductor substrate 101. The electric fuse element 103 is formed on a part of the insulating film 102. The first interlayer insulating film 104 is formed on the insulating film 102 and the electric fuse element 103. The contact holes 105a, 105b extend through the first interlayer insulating film 104 to the second region 103b and the third region 103c, respectively, each of which serves as a contact formation region. The contact plugs 106a, 106b are formed from a conductive material such as tungsten, and fill the contact holes 105a, 105b, respectively. The metal wirings 107a, 107b are formed on a part of the first interlayer insulating film 104 so as to contact the contact plugs 106a, 106b, respectively. The second interlayer insulating film 108 is formed on the first interlayer insulating film 104 so as to cover the metal wirings 107a, 107b. 
In the above conventional electric fuse element 103, however, it is hard to blow the first region 103a which serves as a fuse portion, and therefore a desired resistance value can not be obtained.